Storm Barra: December 7/8th 2021 **Technical Discussion Only**

Winds have backed to SW direction and picking up too. In North Cork

Currently 133 km away From Galway but at the moment from my understanding Galway has now been cleared from the eye at least but Castlebar may have the eye

Pressure of 960hPa at Mace Head lowest i've seen so far, low centre must be close to 955hPa

Serious looking showers at the end of that centre

You could add about 1hpa for every 10m of height for the sea level pressure

A 70 knot gust at Valentia in last hour.

11 am, 10-minute gust 71 knots at Kerry Airport

METAR EIKY 071100Z 24044G71KT 6000 +RA OVC014 06/04 Q0965=

Elsewhere, 67 knots at Sherkin Island the highest

PsMETAR SHER 071100Z AUTO 25047G67KT 3100NDV BKN021/// 08/05 0975 MSL RERA=

Waterford Airport now gusting only 45 knots.

Pressure at Mace Head now 959 hPa.

Cork Airport reported wind speeds... in the last hour it has moderated somewhat ?

GFS 06z showing sustained winds over 80km for Mayo and Sligo tonight - upgrade to a red warning surely?

Hirlam showing this continuing well into Wednesday. I'm using windguru to see those values

Arpege also showing gusts 130 to 150 for Mayo after 6pm. A Red warning would be warranted sooner rather than later so people can get home, make arrangements etc.

Waterford airport gust reports (knots)

9.30 - 57

10.00 - 54

10.30 - 45

11.00 - 55

11.30 - 53

looking at ventusky and they are showing the centre of the storm over Scottish borders tommorrow morning and the north west getting 100kmh gusts. but that's on the icon run . is that an outlier or is that where its heading ?

Valentia was reporting on the aviation site. Gust 70 knots in the previous hour.

PsMETAR VALE 071100Z AUTO 27046G70KT 4000NDV BR BKN017/// 07/05 0971 MSL=

Recent gust to 73 knots or 135km/h at Sherkin Island

"Barra"metric pressure aviation warnings from Met Éireann:

The significance of such warnings is to alert pilots to the danger of gross differences between the indicated altitude (as read from the onboard altimeter) and the actual altitude (true height above sea level, as indicated by e.g. a GPS).

As altimeters are calibrated for use at the standard 1013 hPa, when setting it to the current regional sea-level pressure (QNH) of e.g. 960 hPa, it will read around 1430 feet too high ((1013-960)x27). So if you're flying at what you think is 1500 ft, you're actually only around 70 ft above sea level (and in all likelihood digging a trench in the ground in all but coastal locations).

Cork Airport & Roches Point Wind speeds for today --

956 & rising Knocknacarra Galway. Wind had really dropped but heavy showers

Okay, so let's see how the models did with this from 72 hours ...

This grid with model positions for 12z today was posted in the other thread (now the COVID overflow not storming here thread) on Saturday taking down all available model predictions for the event. Just like in our forecast contests, Con Sensus is almost exactly right.

I have placed an X where the low centre was reported to be (just southwest of Mace Head) and the central pressure was probably closer to 957 than 959. Below this copy of the grid and notes, I have added some comments ...

MODEL PREDICTIONS of 12z TUES 7th DEC LOW position, central pressures

(faster models show an 06z position on the grid (in brackets, e.g. Arp) UK 06z pres likely similar c 965.

Not shown is JMA with low around 53N 18W, similar track to ICON but 12h slower.

==================================================

_ _ _ _ 11_ _ _ _ _ 10 _ _ _ _ _9_ _ _ _ _ _ 8_ _ _ _ _ _ 7_ _ _ _ _ _ 6_ _ _ _ _

_ _ _ _GEMECM _ _ |_ _ _ _ _ _|_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _

______956 957___________________________________________________ 55 F

GFS ICON _ _ con_ |_ _ _ _ _ _|_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _

961 959____X 959__________________Arp__________________________ 54 N

_ _ _(Arp 06) _ _ |_ _ _ _ _ _|_ _ _ _ _ _964 _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _

_____963_(UK)_____________________UK____________________________ 53 N

_ _ _ _ _ _ _ _ _ _ |_ _ _ _ _ _|_ _ _ _ _ _967 _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _

________________________________________________________________ 52 N

_ _ _ _|_ _ _ _ _ _ |_ _ _ _ _ _|_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _ _ |_ _ _ _ _

________________________________________________________________ 51 N

Some earlier model runs had tracks in the 51-52 N area cutting north around 7W,

this is basically off the south coast and then near Wexford.

I have marked a "Con" for consensus on weighted average by model reliability.

That position is near Newport. Most of these model tracks are from WSW to ENE at 12z.

---------------------------------------------------------

The outcome is that the weighted model consensus from 72 hours was very close to perfect. The model which had the least positional error was the ICON which went on to introduce a more southerly track for several runs recently. But back then it had the closest approximation although most of the others were quite good, some were a bit off to the north closer to Belmullet, and the Arpege had a fairly good track but was too fast by about 4-5 hours. The UKMO was the furthest out with a track through west Munster, something it maintained until almost the last run before the storm.

As to intensity, GEM and ECM were closest but the model consensus was also very good.

Moral of the story, take a weighted consensus whenever possible.

Gone very calm here near Castlebar. Reckon the eye of Storm Barra must not be too far away.

Barra certainly cuts quite an impressive picture in the 13.05 satellite image below.